Morphology evolution of thermally annealed polycrystalline thin films

Abstract

Investigation of the morphology evolution of annealed polycrystalline Au(111) films by atomic force microscopy and x-ray diffraction leads to a continuous model that correlates such an evolution to local interactions between grains triggering different mechanisms of stress accommodation (grain zipping and shear strain) and relaxation (gap filling and grain rotation). The model takes into consideration findings concerning the in-plane reorientation of the grains during the coalescence to provide a comprehensive picture of the grain-size dependence of the interactions (underlying the origin of the growth stress in polycrystalline systems); and in particular it sheds light on the postcoalescence compressive stress as a consequence of the kinetic limitations for the reorientation of larger surface structures.

Comment on “Correlation of shape changes of grain surfaces and reversible stress evolution during interruptions of polycrystalline film growth” [Appl. Phys. Lett. 104, 141913 (2014)]

“…The results of Yu and Thompson reproduce well the long-range findings reported by Gonz alez-Gonz alez et al 2 for Au polycrystalline films grown at a homologous temperature of 0.28. In Figure 1(g reveal, as shown in Fig.…”

“…2, reveals that these become shallower (H decreases from 9 down to flat tops, <4 ) as the flux interruption is longer. Local crystallography characterizations of the bundles by surface orientation map (SOM) from AFM images 2 and selected area electron diffraction (SAED) by transmission electron microscopy 5 (TEM, Fig. 1(c)) show that the grains bundled together are orientated to each other with slight misorientations, which suggests that these are separated by pseudocoherent GBs (probably in low-angle and coincident-site-lattice configurations).…”

Compressive intrinsic stress originates in the grain boundaries of dense refractory polycrystalline thin films

“…Differences in the nucleation density on the island tops are also unlikely to lead to large enough differences in the ledge density, as the nucleation density is mainly set by the deposition conditions, which in the present case are identical for all samples. Repulsive forces acting in high angle grain boundaries resulting in unzipping or grooving of these boundaries as suggested by Gonz alez-Gonz alez et al 26,27 can also be ruled out as the grain boundaries are compact throughout the film thickness. It should also be pointed out that the microstructures of the films in the present study are different between the different samples and do not correspond to the structure with grain bundles separated by deep grooves observed in Ref.…”

“…Additionally, experimental data from Magnf€ alt et al 25 have shown a correlation between film density and the compressive stress magnitude in refractory thin films in which atomic mobility during growth is triggered by bombardment with energetic species, suggesting that atom incorporation into grain boundaries generates compressive stress. Another mechanism has been suggested by Gonz alez-Gonz alez et al [26][27][28] who posited that interactions between misoriented grains during island coalescence lead to a film morphology consisting of grain bundles separated by deep grooves. The repulsive forces in the grooves acting on the grain bundles would then result in a compressive strain in the grain bundles and a compressive film stress.…”

Atomistic view on thin film nucleation and growth by using highly ionized and pulsed vapour fluxes

“…Experimental studies have reported that the stress relaxation upon interruption scales with the inverse grain size as predicted by the out-diffusion model [96] but that the stress relaxation does not have the temperature dependence predicted by a diffusion based relaxation process [97,98]. Others have suggested [81,99] that grain rotation coupled with grain boundary diffusion as a cause of the stress relaxation. Alternative explanations for the compressive stress build up include recovery of the Laplace pressure induced stress after coalescence completion [100] and trapping of atoms between surface ledges [73], while stress relaxation has been also attributed to surface flattening and grain growth [100].…”